Current sources are used to supply substantially constant current in electronic devices. For example, certain high speed logic families utilize current sources to generate currents that are switched from one path to another to signify a logical change of state. These types of logic families are generally referred to as current steering logic.
Advantages of current steering logic include very fast switching speed. It can be much faster to switch currents from one path to another than to start and stop currents. Disadvantages of current steering logic include high power consumption. Because the currents are constantly flowing, power consumption does not stop. It would be desirable to efficiently control the current flow in current sources, so as to reduce power consumption where possible. This includes the ability to control only a portion of the total number of current sources in a single integrated circuit.
Prior art approaches to control current sources are exemplified by that of Hsu et. al. described in U.S. Pat. No. 5,142,219, issued Aug. 25, 1992. These prior art approaches include different bias generators for each current source or bank of current sources which is to be independently controlled. It would be desirable to control individual current sources or banks of current sources without requiring different bias generators.
What is needed is an apparatus and method for efficiently and quickly controlling the flow of current in current sources. What is further needed is an apparatus and method for allowing individual control of current sources in an integrated circuit without requiring multiple bias generators.